This invention relates to a map displaying system for displaying map-data on a monitor, like a navigation system and so on.
The navigation system is a system for detecting a user""s standing position by GPS (Global Positioning System) or Self-supporting System, and displaying the standing position together with the surrounding map data on a monitor.
In the navigation system, the displaying method of map data has been improved variously because there is a necessity of comprehending instinctively the situation far way from the standing position. For instance, in the navigation system disclosed in Japanese Patent Laid-open Publication No. 7-220055, as a user is going away from the standing position, the map data is displayed scaling down, and a bird-eye view (a map described looking down on a landscape from the heights) is applied to such displayed map data, said bird-eye view prepared by the conversion processing of perspective projection described later.
The above navigation system, however, adopts 2-dimensional map data, so that the displayed map could be always a 2-dimensional bird-eye view. Accordingly, there was a problem that the user is hard to comprehend the standing position, as the displayed map does not agree with the actual landscape in case of undulating land.
Therefore, in the navigation system disclosed in Japanese Patent Laid-open Publication No. 10-207356, by making a use of 3-dimensional map data the distant place is displayed on a monitor as a 3-dimensional bird-eye view. The configuration will be described below according to FIG. 13.
The 2-dimensional map data storage means 1 stores map data comprising position information and attribute information regarding roads, facilities, town blocks, landmark, and location name. The position information is represented by 2-dimensional coordinates corresponding to the latitude and the longitude.
The landform data storage means 2 stores altitude data of crossing points of the latitude and the longitude per specific degree (distance). That is to say, as shown in FIG. 14, each point represented by a white circle is equivalent to a crossing point of the latitude and the longitude located at a specific distance (degree). The black circles acquired by adding an altitude value to the crossing points are connected with each other, thereby a polyhedron (which is called xe2x80x9cmesh-landformxe2x80x9d hereinafter) is formed. The polyhedron is represented as the undulating conditions of the actual ground surface, that is, the landform (which will be described later).
When the standing position detecting means (the GPS, and so on) that is not shown in the drawings detects a user""s standing position, the 2-dimensional bird-eye view preparing means 3 and the 3-dimensional bird-eye view preparing means 4 are activated and perform the conversion processing of the perspective projection shown in FIG. 15.
In other words, the 2-dimensional bird-eye view preparing means 3 specifies the area (which is called xe2x80x9cplane areaxe2x80x9d hereunder) to be displayed on the monitor as the 2-dimensional bird-eye view at first (in this step, the area to be displayed at the lower side of the monitor is specified), and fetches the map data corresponding to the plane area from the 2-dimensional map data storage means 1. The map data thus fetched out is processed by the converting of the perspective projection, thereby the 2-dimensional bird-eye view data can be prepared.
On the other hand, the 3-dimensional map data preparing means 23 specifies the area (which is called xe2x80x9csolid areaxe2x80x9d hereunder) to be displayed on the monitor as the 3-dimensional bird-eye view at first (in this step, the area to be displayed at the upper side of the monitor is specified), and fetches the map data corresponding to the solid area from the 2-dimensional map data storage means 1 while fetching the altitude data in the solid area from the landform data storage means 2. After preparing the 3-dimensional map data as shown in FIG. 16 in accordance with the map data and the altitude data fetched out as above, the 3-dimensional bird-eye view preparing means 4 prepares the 3-dimensional bird-eye view data by the conversion processing of the perspective projection on the display coordinate system.
After the 2-dimensional bird-eye view data and the 3-dimensional bird-eye view data are prepared as above, the display means 5 displays the 2-dimensional bird-eye view data at the lower side of the monitor and the 3-dimensional bird-eye view data at the upper side of the monitor (see FIG. 17).
In the above description, the 2-dimensional map data is handled as one data including roads, facilities and etc., but when the road data should be main like a car-navigator, it is configured that road information are displayed being overlapped on the map information displayed as above.
Specifically, the 2-dimensional road data storage means 21 (which may be included in the 2-dimensional map data storage means) stores various information regarding roads as the 2-dimensional road data. The 2-dimensional road data comprises xe2x80x9cpoint number informationxe2x80x9d for specifying each point composing a road (which is called xe2x80x9croad component pointxe2x80x9d hereafter), xe2x80x9clatitude and longitude informationxe2x80x9d for expressing the latitude and the longitude at which the road component point is located by the corresponding 2-dimensional coordinates (x-coordinate, y-coordinate), xe2x80x9croad type informationxe2x80x9d for indicating the type of the road such as ROUTE X, xe2x80x9cconnection informationxe2x80x9d for expressing the road component points to be connected by the above-mentioned point number, and so on. And as shown in FIG. 18(a), a Point 2(x, y)=(100, xe2x88x92100), said point composing ROUTE 16 by being connected with a Point 3, may be represented by the 2-dimensional road data, such as (2, 100, xe2x88x92100, ROUTE 16, 3) [point number information, x-coordinate, y-coordinate, road number, point number information of the next connected point].
Here, providing that the map information should be converted to the 3-dimensional bird-eye view as described above, the problem is how to overlap the landform data with the road information.
As shown in FIG. 13, the 3-dimensional road data preparing means 22 first specifies an area to be displayed based on the standing position, and the 2-dimensional road data corresponding to the displayed area is fetched out from the 2-dimensional road data storage means 21 while the landform data corresponding to the displayed area is fetched out from the landform data storage means 2. Moreover the 3-dimensional road data is prepared based on the 2-dimensional road data and the altitude data fetched out as above. The converting of the perspective projection is performed on the 3-dimensional road data.
Thereby, the ground surface image data and the 3-dimensional road image data are prepared. Such data are combined to the bird-eye view by the 3-dimensional bird-eye view preparing means 4, and then handed to the display means 5.
As a result, the monitor can display the image combining the ground surface image data and the 3-dimensional road image data even the solid data.
The navigation system disclosed in Japanese Patent Laid-open Publication No. 10-207356, however, is configured to prepare the 2-dimensional bird-eye view data based on only the 2-dimensional map data (which is not based on the altitude data). That is to say, although the actual altitude value is adopted as an altitude value of the solid area B, since 0 is used as the altitude value of the plane area, accordingly it causes a problem; the sudden altitude difference appears in the boundary between the 2-dimensional bird-eye view and the 3-dimensional bird-eye view, as shown in FIG. 17.
And in the conventional navigation system, it is configured that the 3-dimensional road data is prepared only by connecting the road component points one after another with a straight line. Therefore, when there are the road component points dispersed from one mesh to another as shown in FIG. 19, it is not possible to display the ground road along the undulation of mesh-landform. This problem appears remarkably on the part of the straight line on which the density of road component points is lower than that of the changeful part such as a curve.
And moreover, since it is defined that the road component points exist on the surface of the earth in the above conventional navigation system, even the underground road such as a tunnel must be described on the surface of the earth, otherwise the underground road is not described at all. Therefore, such configuration is not convenient for the user.
The present invention is suggested based on the above conventional problems, and has an object to provide a map displaying system that can display continuously both the 2-dimensional bird-eye view and the 3-dimensional bird-eye view, and also display the ground road along the undulation of the mesh-landform, moreover display not only the ground road but also the underground road.
To achieve the object, the invention adopts the following means. Specifically, the invention presupposes the map displaying system, as shown in FIG. 1, for displaying a 2-dimensional bird-eye view acquired by the perspective processing of map data in a plane area represented by 2-dimensional coordinates, and for displaying a 3-dimensional bird-eye view acquired by the perspective processing of 3-dimensional map data in a solid area made by adding altitude values to plural points of map data represented by the 2-dimensional coordinates.
And the reference altitude value determining means 6 determines as a reference altitude value the altitude data in each specified area, such as, the mean value of the altitude data in the plane area, the mean value of the altitude data in the boundary area between the plane area and the solid area, and so on.
According to the reference altitude data, the altitude data changing means 7 changes the altitude difference between the plane area and the solid area B to relative height of a user""s sight. In other words, the altitude data changing means 7 changes the altitude data in the solid area B into the value made by subtracting the reference altitude value from the true altitude data, and when the changed value gets negative, the negative value is handled as 0.
According to the prescribed procedure, it is possible to display the 2-dimensional bird-eye view and the 3-dimensional bird-eye view continuously (see FIG. 4).
Moreover, without using the reference altitude value as described above, the following processing can be adopted. That is to say, it is configured as shown in FIG. 7 that altitude data changing means may interpolate a gap formed in the boundary between the plane area and the solid area and may bring the continuity to the plane area and the solid area. In this case, the altitude data changing means makes an altitude vale compulsively equal to either an altitude value in the boundary of the plane area side or one in the boundary of the solid area side, said both side boundaries forming the gap, and smoothes those altitude values so as to diminish the moving volume form the original altitude value along with going away from the boundary.
And a method of displaying a 3-dimensional road in the map displaying system is as follow.
3-dimensional road data preparing means may interpolate by adding an altitude to specific points on respective straight line connecting road component points. Thereby the road information composed by the road component points can match the landform data composed by altitude data and a specific rectangular such as the latitude and longitude.
In case of displaying the underground road data, 2-dimensional road data storage means stores 2-dimensional ground road data and 2-dimensional underground road data separately; and 3-dimensional underground road data preparing means prepares 3-dimensional ground road data based on the 2-dimensional ground road data and the altitude data, and prepares 3-dimensional underground road data based on the 2-dimensional underground road data and the altitude data.
In this case, the 3-dimensional underground road data preparing means calculates the altitude value of the road component points located under the ground in accordance with a straight line connecting a start point and an end point, if both the start point and the end point of the underground road are known. And on the other hand, the 3-dimensional underground road data preparing means calculates the altitude value of the road component points located under the ground in accordance with the altitude value on the ground corresponding to the road component point, if either the start point or the end point of the underground road is known.
Therefore, it is possible to display on a monitor not only the 3-dimensional ground road but also the 3-dimensional underground; the invention can provide a user with a map displaying system useful by far.